Hydro-Fins for Increasing Maneuverability and Speed

ABSTRACT

The fields of application of the present invention is within the industry related to the manufacturing of nautical/marine and sport equipment, and more precisely to the field of fins design for any type of board within a fluid environment. The novelties of the Spinfins, compared to traditional fin designs, are: (i) the curvature in the vertical direction permits the fin to have sufficient surface exposed to the fluid to ensure directional control but its lower height yields to a lower drag in the direction of the motion and consequently is faster than traditional fins; and (ii) the angle of twist in the vertical direction of the fin permits to modify the leading and trailing edges angles relative to the flow resulting in a more uniform pressure on the concave surface of the fin. The more uniform pressure on the concave surface makes the force exerted by the fin more efficient throughout a turn.

SPECIFICATION

This product is related to the fin design used in hydro-sports for control, steering and stability of any type of board, and does not include any fin designed used in any rotatory mechanism utilized for propulsion to generate work or power. The innovative fin designed includes a curvature (not straight) to increase surface exposed to the fluid and a twist, may or may not be present, to ensure a more uniform pressure throughout the fin's surface. These modifications represent an innovation in the actual state of the hydro-sports fin design and would be described in detail in this document. The main contribution of these modifications is to greatly increase the maneuverability and speed as compared to traditional fins. This invention applies to any type of board that it is used to slide on the water. The primary sports of application of these products are in surfing, SPS, wake, water skiing, windsurf and kite surfing.

TECHNICAL FIELD

In the rest of this document the Hydro-Fins would be referred as Spinfins. This application claims the benefit of the Spinfins as to compare to traditional fin designs. The benefit would be presented using kinematics, kinetics and computational fluid dynamics along with the physics involved in hydro-dynamics activities. Even though, the basic principles apply to almost any water sport involving a board equipped with fin(s), the analysis and discussion herein will focus on surfing.

The fields of application of the present invention is within the industry related to the manufacturing of nautical and sport equipment, and more precisely to the field of fins design for any type of board within a liquid environment.

BACKGROUND

In order to show the novelty of the present products, referred as SpinFins, it is necessary to briefly describe the major fin evolution through time. For brevity, the fins evolution is restricted to the shape of the fins and does not include the evolution of the fins configuration (how the fins are placed under the board).

The first records of surfing go back many centuries when Polynesian civilizations rode their long wood surf boards without any type of fins. The surfer had to control the board with the sides of the board or by using his/her body extremities (hand or foot).

In 1935, Tom Blake equipped for the first time in history a surf board with shallow, long based fin. The fin greatly decreased the velocity of the board and offered a pivot point to control and maneuver the board. Until the 1960, inspired by the dolphin and black fish dorsal fins, surf fins change their general shape and the overall height was initially increased to increase stability [2].

For the next decades, the major advances in the surfing industry were due to new materials. Surfboards switch from being solid wood, to hallow plywood, to the modern foam fiberglass boards. A similar occur with the fins that transitioned from wood, to metal and finally to composite materials.

In summary, all present fins' design have different shapes simulating dorsal fins of fish/mammals but are in most cases vertical and do not present any curvature or twist in the vertical direction. However, some fins present a lateral deflection at the tip in both directions to simulate a hydro-foil, or a rounded curvature in a section of the vertical direction in order to create a tunneling effect.

To the best knowledge of the author, it does not exist any fin that presents the geometry and characteristics of the Spinfins in order to enhance maneuverability and speed of the sliding board. The only reason of the curvature in the Spinfins is to increase the surface area exposed to the water without increasing the height of the fin, and not creating the tunnel effect. No single fin presents any twist from based to tip in the vertical direction.

SUMMARY OF INVENTION

This product is related to the fin design used in hydro-sports for control, steering and stability of any type of board, and does not include any tin designed used in any rotatory mechanism utilized for propulsion to generate work or power. The fin designed includes a curvature in the vertical direction. The vertical direction is defined as the perpendicular direction from the attached position of the fins on the board. The curvature of the tin can be defined as either being concave on the inside part or convex on its outside part. An angle of twist of the fin about its vertical direction may or may not be present depending on the application of the fin. The angle orientation of the twist can either be counter-clockwise or clockwise.

The new fin shape design majorly has three different characteristics as to compare to traditional fins:

1) the constant concave curvature of the blade increases the side surface area of the fin without increasing its total height. This characteristics gives enough stability to the board but highly increases its maneuverability due to the fact that by having a lower height it is easier for the operator (surfer) to release the fins from the water to perform extreme maneuvers.

2) the lower height (vertical) greatly decreases the drag coefficient in the direction of the motion resulting in higher board velocity

3) the twist of the blade, may or not be present, provides a more uniform pressure of the water on the inside surface of the fin throughout the turns. This characteristic makes the fin more efficient than traditional tins that tend to resist the turn at the trailing edge while executing the maneuver. Some fin manufacturers are trying to create a similar effect by changing the flexibility of the fin (make it more flexible) at the trailing edge.

TECHNICAL PROBLEM

To coherently describe the benefits of a fin compare to another one is practically impossible for it depends on the characteristics of the rider (surfer), the placement of the fin on the board, the flow velocity, and the maneuver to be performed among other parameters. However, in order to have a fair comparison between traditional fins and the Spinfins the same flow velocity, flow angle of attach, and flow properties would be considered. In this work, the performance of the fins is described by the values of the drag (resistance of board to moving flow) and the lift (side force) coefficients given by the equations:

${{Drag}\mspace{14mu} {coefficient}},{C_{d} = \frac{D}{q \cdot A}}$ ${{Lift}\mspace{14mu} {coefficient}},{C_{L} = \frac{L}{q \cdot A}}$

D is the drag force, L is the lift force, A is exposed area and q is the dynamic pressure given by q=1/2ρv² where ρ is the water density (998 kg/m³) and v the water flow velocity.

The Computational Fluid Dynamic (CFD) model constructed to justify some of the claims in this application is pressure based using the SST k-omega-epsilon turbulent flow model with the SIMPLEC scheme for numerical solution. For comparison purposes, results are presented for the side fins and a traditional fin, referred as Ref. The exposed area used is the one of reference fin and it is equal to 0.028 m². For the reader reference, the exposed area of the SpinFins is 0.015 m².

CITATION LIST

-   [1] http://www.thefinbox.com/history/history-of-the-fin/ -   [2]     http://www.surfinghandbook.com/surfboard-design/surfboard-fins/surfboard-fin-history/ -   [3] http://www.surfresearch.com.au/f.html -   [4] http://www.aufins.com/

BRIEF DESCRIPTION OF DRAWINGS

In order to facilitate a fuller understanding of the present invention, reference is new made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only:

FIGS. 1A-1D is schematic representation of a reference fin to be used for comparison purposes.

FIG. 2 is a schematic of the reference fin and an exemplary Spinfins.

FIGS. 3A-3D is a schematic of the side Spinfins from different views.

FIGS. 4A-4D is a schematic of the center Spinfins from different views.

FIGS. 5A-5C is a schematic of an exemplary fin indicating how the twist of the Spinfin is defined.

FIG. 6 is the plot of C_(d) Vs. Angle of Attack for reference and exemplary Spinfins.

FIG. 7 is the plot of C_(L) Vs. Angle of Attack for reference and exemplary Spinfins.

FIG. 8 is the plot of C_(L)/C_(d) Vs. Angle of Attack for reference and exemplary Spinfins.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1A shows the geometry of a traditional side fin that is used as a reference and comparison object for the present patent application. The figure shows the side view of the reference fin with the general terminology used to describe a fin. The base is defined as the distance between the leading edge to the trailing edge of the fin. The depth is the distance from the base to the maximum distance of the fin in the vertical direction. The sweep is the measurement that defines how far back the fin curves in relation to its base.

FIG. 1B shows the front view of the reference fin and it clearly indicates that the reference fin, like most all fins, do not have any curvature in the vertical direction.

FIG. 1C shows the isometric view of the reference fin with a demarcation for the detailed view of the cross section.

FIG. 1D shows the detailed view of the cross section. The figure indicated that contour shape of the cross section follows a foil geometry. Foil refers to the shape of the outside and inside faces of the fin, thinnest near the tip and thicker near the base. Foil alters the flow of the water over the fin surface and has a direct impact on the performance of your fins and board. Middle fins are always symmetrical and convex on both sides (50/50) for even distribution and stability, while outside fins are usually convex on the outside face and flat or curved on the inside. A flat inside face creates a solid balance of control, speed, and playfulness, while a curved or concave inside face maximizes lift with minimal drag, ideal for speed generation and fluidity.

FIG. 2 shows the side view of the reference fin and Spinfins at a 1:1 scale. It is clear that both fins have a similar base but the depth is very different. The difference in depth is the major factor for the Spinfins to have a smaller drag coefficient than the reference fin.

FIG. 3A shows the side view of the side Spinfins. The contour of the fin is defined as the line that creates a close surface from the leading edge to the trailing edge by passing through the tip.

FIG. 3B shows that iri the vertical direction of the side Spinfins has a concave (inside) and/or convex (outside) curvature in the vertical direction that does not exist for the reference fin. The curvature in the vertical direction is between 0.5-10 degrees and is defined by the line joining the fiat curve of the base with the point at the tip of the fin.

FIG. 3C shows the isometric view of the side Spinfins and the cant angle is shown in the figure. The cant angle is defined as the angle between the chord line and the line joining the chord line to the apex of the fin.

FIG. 3D shows the top view of the side Spinfins and helps to show the concave curvature of the fin in the vertical direction.

FIG. 4A shows the side view of the center Spinfins. Basically, the center fin was defined as two side Spinfins connected on their concave side (outside).

FIG. 4B shows that in the vertical direction of the center Spinfins has two concave surfaces and a cant angle defined as the angle made by a line connecting the chord of the fin to the apex of the fin.

FIG. 4C shows the isometric view of the center Spinfins.

FIG. 4D shows the top view of the center Spinfins and helps to show the two concave curvature of the fin in the vertical direction.

FIG. 5A-5C shows a cut of the side Spinfins in order to more clearly indicate the angle of twist about the vertical direction. The angle of twist is defined as the rotation of the Spinfins about its vertical direction. Values for the angle of twist are relatively small and should never exceed 15 degrees.

FIG. 6 shows the drag coefficient C_(d) in the flow direction (x-direction) versus different angle of attack for the Reference and Spinfins. The figure indicates the resistance coefficient of the fin to move in the direction of the flow when the angle of attack varies between 0 to 90 degrees. The angle of attack is defined as the angle between the chord of the fin foil and the direction of the flow. The chord is the imaginary straight line connecting the leading edge e to the trailing edge.

FIG. 7 shows the lift coefficient C_(L) in the flow direction versus different angle of attack. For a hydrofoil the lift is defined as the force perpendicular the inside/outside of the fin that is produced by the motion of the fin in the fluid. The higher the lift coefficient, the more effective is the fin to generate lateral force.

FIG. 8 shows the drag coefficient C_(L)/C_(d) in the flow direction versus different angle of attack. The ratio C_(L)/C_(d) is an indication of the fin efficiency. 

1. The side-Spinfins have a curvature starting from the chord line at the asymmetric base of the fin and extending to the tip of the fin. The side-Spinfins has a continuous convex defbrmation in the vertical direction while the outside surface has a constant concave deformation.
 2. The center-Spinfins is two side-Spinfins put together from their concave outside surface. The two side-fins put together create a symmetric foil at the base and a continuous curvature goes from center line (chord lide) to the point where the two side fins are not connected any longer. From that location to the tip the two extremities keep their unsymmetric foil cross-section.
 3. Spinfins are the only fins that have a twist about the vertical axis. The angle of twist can be counterclockwise or clockwise modifying the angle of attack of the leading edge in the chord wise direction. The angle of twist create a variable angle of attack in the chord wise direction
 4. Spinfins twist angle allows to have a more uniform pressure on the inside of the fin throughout a turn as compared to vertical fins. 